Digital Subscriber Line (DSL) technologies, such as Asymmetric DSL (ADSL) and Very High Speed DSL (VDSL), provide a large amount of communication bandwidth using existing twisted-pair telephone subscriber lines. When transmitting data over the subscriber lines, DSL technologies typically use a Discrete Multi-Tone (DMT) line code that assigns a number of bits to each tone or sub-carrier. The DMT may be adjusted to various channel conditions that may occur during training and initialization of the modems at each end of a subscriber line.
Data signals transmitted over subscriber lines may be significantly degraded by impulse noise interferences generated by external sources. For example, refrigerators, hairdryers, dimmers, and other electrical equipment at the customer premises generate impulse noises when they are turned on or draw additional power. The electrical interference generated by these impulse noise events may cause burst errors in the DSL data transmissions. To ensure reliable data transmission, the various DSL specifications define certain levels of impulse noise protection (INP). Higher INP levels provide lower error rates, but at the cost of reduced transmission rates.